Disposable absorbent articles are well known and all have absorbent elements for absorbing and retaining body fluids; an absorbent element must be able to acquire liquid rapidly and to distribute it internally so as to prevent leakage and must also have a good capacity to retain the fluids when subjected to the normal pressures of use.
Whilst the primary focus of absorbent articles remains the ability of these articles to absorb and retain fluids, another important area of development in this field is the control of odourous compounds contained within the absorbed fluids or their degradation products. There are a wide range of compounds which may be present in an absorbent article during use which result in the formation of malodourous. These compounds include fatty acids, ammonia, amines, sulphur containing compounds and ketones and aldehydes.
The art is replete with descriptions of various odour control agents for use in absorbent articles in order to address the problem of malodour formation. For example, acidic, basic and neutral odour control agents are known.
Odour control means comprising mixtures of different types of odour control agents are widely used in absorbent articles in order to increase the effectiveness of the odour control means against the various malodorous compounds associated with the use of absorbent articles following the absorption of aqueous body fluids.
For example EPO 348978 discloses an absorbent article comprising an odour control system wherein the neutral odour control particles are selected from carbon, clays, silica, zeolites and molecular sieves. WO 91/12029 discloses the combination of zeolites and absorbent gelling materials to provide improvement in the control of ammonia odours.
Although mixtures of different odour control agents can perform well their action in controlling the odours associated with the use of absorbent articles, interactions between certain odour control agents and the absorb ed aqueous body fluids, or between different odour control agents can at least partially impair the effectiveness of known odour control means.
U.S. Pat. No. 5,230,958 describes a process for incorporating an odour control means in powder form into a hydrophilic, swellable, water-insoluble polymer, in order to get a flexible structure containing the odour control particles in a dust-free stable form. Possible interactions between two incompatible odour control agents can be avoided by incorporating these odour control agents separately in two different substrates of the structure.
The odour control compounds described in the patent typically perform their action when liquid is absorbed by the hydrophilic polymer that incorporates them, and therefore liquid cannot be prevented from reaching those odour control compounds that can be negatively influenced by absorbed liquid.
U.S. Pat. No. 5,037,412 describes a sanitary article in which odour control agents of acidic, basic and neutral type that are active preferably in their anhydrous state are incorporated in such a way that they are not reached by absorbed fluid, and therefore remain substantially dry, for at least a substantial period of time after absorption of fluid by the sanitary article. The odour control agents are mixed together and positioned in the sanitary article at locations that are not likely to be reached by the absorbed fluid for a substantial period of time after absorption, e.g. between the absorbent core and the backsheet, along the periphery of the backsheet itself, or in the centre of the absorbent core, or even along its periphery.
While these structures are capable of avoiding interactions between absorbed fluids and odour control agents that can be negatively influenced by them, they have a rather complex structure, while at the same time the odour control means is a simple mixture of different odour control agents, all of them intended to act in their dry state.
In European Application EP-A-510619 an absorbent article is described which comprises an odour control complex including a combination of at least 2 agents selected form a group which includes zeolites and silica gels. The effectiveness of at least some of the odour control agents can be enhanced by disposing the liquid absorbent material, typically a fluff of cellulose fibres, between the topsheet and the odour control agents themselves, in order to reduce the exposure of the agents to body fluids. The structures described are fairly complex and rely on a combination of several different components and odour control agents each performing one different task among fluid absorption, pH buffering, and odour controlling. Moreover, when odour control agents are incorporated in these structures in particulate form, it is difficult to avoid loss or spillage of these particles from the structure, both during the production, and during the use within the sanitary product that incorporate it. These structures are therefore not suitable for production as a semi-finished product intended to be sold and stored separately in form of a continuous web-like structure, e.g. wound in a roll, which can subsequently be fed to a production line of sanitary articles.
Hence, there still exists a need to provide an absorbent structure that comprises an odour control means and is simple to produce while having a better effectiveness. It has now been observed that this need can be addressed by an absorbent structure in which a combined synergic effect is achieved between absorbent gelling material and different odour control agents, by which the performances of the odour control agents that act preferably in dry conditions, and optionally of those that are active in solution, are enhanced. The structures also take advantage of the combined activity of its components in performing two or more actions among fluid absorption, pH buffering, and odour control. Moreover, they can be produced as a semi-finished product, while being substantially free from loss or spillage of incorporated particulate material.